A half bridge type modular multilevel converter, which is a conventional power converter, includes three phase modules connected in parallel between a positive voltage terminal and a negative voltage terminal. Each of the phase modules includes: a first arm connected between the positive voltage terminal and an AC terminal; and a second arm connected between the AC terminal and the negative voltage terminal, each of the first and second arms including a plurality of unit cells connected in cascade.
Each of the unit cells includes: a capacitor configured to be charged to a DC voltage; first and second switching elements connected in series between positive electrode and negative electrode of the capacitor; and first and second diodes respectively connected to the first and second switching elements in antiparallel. In each of the arms, the second switching elements of the plurality of unit cells are connected in series. By controlling the plurality of unit cells in each of the arms, one of DC power and three-phase AC power can be converted into the other of the DC power and the three-phase AC power (for example, see Patent Document 1 (Japanese Patent Laying-Open No. 2012-228025)).